The seeds of many fruits such as legumes, grains, silques and drupes are comprised of a meat that is covered by a skin or seed coat (the term "seed" as used herein will be intended to include the seeds of products such as legumes, grains, drupes, achenes, silques and other types of seeds used for food products). Beans, corn, and coffee beans are examples of seeds from legumes, grains, and drupes, respectively. Rape seed is one example of seed which comes from silques. Sunflower seeds and buckwheat are seeds which come from a type of fruit called an achene.
A nut is a one-seeded fruit which, for purposes of this application will be referred to as a "seed". The nut kernel, which is the component of the nut that remains after shelling, is comprised of a nut meat that is covered by a brownish skin. Skinning of a nut kernel is commonly referred to as "blanching."
Removal of the skin or hull for such seeds is desired for a variety of reasons. For example, some skins, such as those found on coffee beans, hazelnuts, and Brazil nuts have unpleasant bitter tastes. For other seeds, such as almonds, removal of the skin is desired to prevent the skin from coloring foods that are prepared using the seeds. Skin or hull removal for seeds in the grain family, such as wheat and corn, is desired for the production of certain grain products such as wheat flour and masa. It is also desirable to remove the skin or hull from certain seeds so that the skin or hull may be used as dietary fiber for humans or other animals.
Various processes have been used for removing the skin from seeds. These processes have enjoyed limited success. For the most part, existing processes are unsatisfactory because they do not completely remove the skin without abrading away significant amounts of meat or because they involve temperatures or substances which adversely affect the taste, appearance or shelf life of the seeds.
Because many seeds are small in size, it is difficult to abrade the skins from the seeds without significant loss of meat. Mechanical abrasion of these seeds may result in loss of a substantial portion of the valuable seed meat. Certain nuts, such as hazelnuts and Brazil nuts, have a tightly adhering skin which is difficult to remove due to deeply embedded vein networks. The convoluted surfaces of these and other nuts, such as almonds, make it difficult to abrade the skins from the nuts without significant loss of nut meat. Often mechanical abrasion of these nuts results in a loss of 10 to 20% of the valuable nut meat.
Some existing processes for skinning seeds involve removing the skins by high pressure jets of water or by scalding water. Unfortunately, high water pressure also may erode areas of the meat and create pits in the surface of the seeds. Breakage is also known to occur, which is particularly undesirable for products which are marketed in whole form. Further, seeds treated with these methods tend to absorb water and thus require drying, a process which can weaken the flavor of the seeds.
The skins of corn and beans such as red beans, broad beans and peas are often removed after the products have been boiled, because boiling loosens the skins of these products. This process causes the beans to absorb water and thus has limited applicability in contexts where a dryer product is desired. The hulls of coffee beans are commonly removed using pneumatic separators, which are sometimes unsuccessful at completely removing the hulls, or by soaking which requires substantial drying time following soaking.
In a common chemical process for removing skins from some seeds such as nuts, seeds are first immersed in an alkaline bath, subsequently immersed in an acid bath, and finally subjected to mechanical abrasion. However, the acid leaves the seeds with an unpleasant bitter taste and may reduce their shelf life. Moreover, the concentrations of the chemical solutions dilute over the soaking period because of debris introduced into the solutions by the seeds. Dilution makes regulation of the concentration of the solutions highly difficult and renders these processes unfeasible for large scale blanching operations.
Some products are skinned using hot caustic soaking. In hot caustic soaking, the products are soaked in hot (i.e. approximately 180.degree. F.) sodium hydroxide solution and subsequently peeled using mechanical abrasion. During soaking the hot caustic penetrates below the skin, softening the flesh underlying the skin. This softened flesh is abraded away during the mechanical peeling step, resulting in loss of valuable product. Moreover, use of sodium hydroxide--a caustic agent frequently referred to as lye--produces toxic effluents which, for environmental reasons, are difficult to dispose of. Processes using lye are strongly alkaline and produce unstable alkaline solutions above pH 9 which require neutralization before final disposal.
Finally some seed products, such as hazelnuts, are skinned by roasting followed by light mechanical abrasion of the skins from the seeds. Although this method is satisfactory at removing the skins, it produces seeds having a roasted flavor.